A British novelist has said “painfully thin” Kate Middleton has no personality, and her only purpose is to breed.

Hilary Mantel, a double Booker Prize-winner, also said the Duchess of Cambridge was “machine-made” compared to Princess Diana, reported the Sydney Morning Herald.

"Kate seems to have been selected for her role of princess because she was irreproachable: As painfully thin as anyone could wish, without quirks, without oddities, without the risk of the emergence of character,” said Mantel in a lecture at the British Museum.

"She appears precision-made, machine-made, so different from Diana whose human awkwardness and emotional incontinence showed in her every gesture."

She said Middleton would become a “jointed doll on which certain rags are hung”, as she would be only defined by what she wore.

"These days she is a mother-to-be, and draped in another set of threadbare attributions. Once she gets over being sick, the press will find that she is radiant,” said Mantel.

"They will find that this young woman's life until now was nothing, her only point and purpose being to give birth."

Mantel said Paul Emsley’s official portrait of Middleton showed a woman with “dead” eyes.